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Exchange-enhanced reactivity in bond activation by metal–oxo enzymes and synthetic reagents

Nature Chemistry volume 3, pages 19–27 (2011)Cite this article

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A Corrigendum to this article was published on 22 May 2012

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Abstract

Reactivity principles based on orbital overlap and bonding/antibonding interactions are well established to describe the reactivity of organic species, and atomic structures are typically predicted by Hund's rules to have maximum single-electron occupancy of degenerate orbitals in the ground state. Here, we extend the role of exchange to transition states and discuss how, for reactions and kinetics of bioinorganic species, the analogue of Hund's rules is exchange-controlled reactivity. Pathways that increase the number of unpaired and spin-identical electrons on a metal centre will be favoured by exchange stabilization. Such exchange-enhanced reactivity endows transition states with a stereochemistry different from that observed in cases that are not exchange-enhanced, and is in good agreement with the reactivity observed for iron-based enzymes and synthetic analogues. We discuss the interplay between orbital- and exchange-controlled principles, and how this depends on the identity of the transition metal, its oxidation number and its coordination sphere.

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Figure 1: Gas-phase energy profiles calculated with B3LYP.
Figure 2: Orbital occupancy-evolution diagrams during H-abstraction processes and corresponding orbital-selection rules for predicting transition state structures.
Figure 3: Energy profiles and orbital occupancy-evolution diagrams.

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  • 18 April 2012

    In the version of this Article originally published, in Fig. 1d the energy levels 4P and 6P were interchanged. Also, the start of the final sentence of the section "Interplay of exchange and orbital promotion energies" should have read: "Finally, S= 5/2 becomes virtually degenerate with the ground state...". These errors have been corrected in the online versions of the Article.

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Acknowledgements

This research is supported by an ISF grant to S.S. (ISF 53/09). Collaborations (since 2005) with L. Que and W. Nam are gratefully acknowledged.

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  1. Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel

    Sason Shaik, Hui Chen & Deepa Janardanan

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  1. Sason Shaik
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Correspondence to Sason Shaik.

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Shaik, S., Chen, H. & Janardanan, D. Exchange-enhanced reactivity in bond activation by metal–oxo enzymes and synthetic reagents. Nature Chem 3, 19–27 (2011). https://doi.org/10.1038/nchem.943

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